Method to start up and manage a combined cycle thermal plant for energy production and relative plant

ABSTRACT

A method to start up and manage a combined cycle thermal plant for energy production comprising the execution according to a set sequence of a plurality of functional groups.

The present invention refers to a method for the start up and management of a combined cycle thermal plant for energy production according to the preamble of claim 1.

Within the range of the present invention, expressions like “functional group” and similar expressions indicate a precisely set sequence of successive operations automatically operated and linked between them; substantially said expressions are used to indicate a macroinstruction formed by a plurality of minor instructions linked between them both functionally and temporally.

Furthermore, within the range of the present invention the term “bottling” when referred to a recovery steam generator is used to indicate a series of activities as a whole destined to insulate the steam generator itself and its thermal cycle as much as possible from the outer environment and further components with a view to keep all the accumulated heat inside. The bottling operation is carried out by appropriately operating on the insulating systems of the plant (valves, dampers, etc.).

Plants for the production of electric energy of the above specified type, are also known as combined cycle plants since they have a recovery steam cycle subordinate to a first thermal cycle through which they generate electric energy by exploiting one or more gas and generator turbine groups. These plant are widespread nowadays thanks to their high flexibility of use allowing to change within a very large percentage range and in a reasonable lapse of time the quantity of energy produced, while maintaining a good total efficiency when the plant has reached substantial operating conditions.

Furthermore, it is pointed out that combined cycle thermal plants for the production of electric energy can be stopped and started up again within a reduced lapse of time.

A very critical state for combined cycle plants for the production of electric energy is the so called transient state, i.e. the phases where the plant changes its operational status. Transient states during the plant functioning may be:

-   -   the start-up of the plant from an off-state when starting only         one gas turbine and generator group and the following warm up         and load increase of TV steam turbine;     -   the start-up of the second gas turbine and generator group while         both the first gas turbine and generator group and the steam         turbine are already working;     -   the total halt of the plant starting form an initial condition         where only one gas turbine and generator group is working or     -   the halt of a gas turbine and generator group starting form an         initial condition where two gas turbine and generator groups are         working.

It is almost unnecessary to remark that aforementioned transient states during the plant functioning are critical from the point of view of:

-   -   1. the structural stresses of the components (for instance         because of the heavy working conditions or of the sudden thermal         changes by several hundreds of degrees to be absorbed within few         hours) and     -   2. the uncertainty and decisional discrimination of the operator         when the start-up is carried out as a sequence of manual         operations instead of automatically.

Moreover, the transient states are critical even when considering the total efficiency of the plant, namely during the start-up phases.

Furthermore, it must be underlined how the greater part of pollution emissions are freed during the transient state of the plant starting from an off-state.

From the above said it highlights the need to operate the plant with start-up and stop sequences which:

-   -   are highly optimized, in order to reduce the mechanical and         thermal stress of the components,     -   allow reducing to the lowest terms the duration of the transient         state without weighing upon the whole efficiency of the plant         and     -   reduce to a minimum the incidental mistakes by limiting as much         as possible the operator's discrimination. Granted that for each         plant component, such as, for instance, the generator and gas         turbine group, the steam generator or the steam turbine a         specific functional group must be implemented, i.e. a well         determined sequence of successive operations, for the start-up         or stopping foreseen by the producer of the component itself,         with a view to guarantee said need we now have the problem to         link correctly between them the functional groups of the         different components of the plant in order to have a concerted         start-up or stopping procedure to make the plant turn from a         first state, for instance from an off-state, into a second         state, for instance an operating plant.

Nowadays, said concerted implementation of the correct sequence of functional groups depends on the technicians' experience who follow and implement a written sequence of functional groups conceived on purpose for a specific plant. To this respect it is useful to underline that, even when formally correct as for the linkage, the functional groups sequence is carried out according to the timing decided step by step by the plant technician who, judging from his personal experience, and evaluating from time to time the specific physical and operational parameters detected in the plant, decides on the basis of his personal experience which are the operations to switch on the different components involved in the start-up.

This procedure is not satisfactory both because it requires the attendance of a plant technician having a long experience with the specific plant to be started/stopped and because, it goes without saying, different technicians will implement different start-up timings which, even though correct, do not always allow optimizing the procedure and, at the same time, satisfying said need.

The problem at the basis of the present invention is that of devising and developing a method to optimize the start up and/or stopping sequences, partially or totally, of combined cycle thermal plants for the production of electric energy once the functional groups known, i.e. the specific operations to be carried out to operate the start up or the stopping of the specific components of the plant. This problem is solved by a method for the start up and management of a combined cycle thermal plant for energy production according to claim 1.

According to a further aspect, said problem is also solved by a combined cycle thermal plant for energy production according to claim 7, being suitable to implement the following method.

Further features and advantages of the method according to this invention and of the plant according to this invention will enhance from the description hereinafter detailed of some preferred example embodiments thereof, given for indicating and not limiting purposes, with reference to FIG. 1 representing a schematic and diagram view of a combined cycle thermal plant for energy production wherein to implement the method according to this invention.

According to the above stated, the thermal plant for energy production comprises:

-   -   a first gas turbine and generator group TG1,     -   A first recovery steam generator GRV1 to regenerate the latent         heat of the exhaust gases of said first gas turbine and         generator group TG1;     -   a second gas turbine and generator group TG2,     -   a second recovery steam generator GRV2 to regenerate the latent         heat of the exhaust gases of said second gas turbine and         generator group TG2;     -   a steam turbine TV with low, medium and high pressure stages         being in fluid communication with the first steam generator GRV1         through steam lines at high, medium and low pressure,         respectively AP, MP and BP;     -   a high pressure steam collector CAP, a medium pressure steam         collector CMP and a low pressure steam collector CBP to create a         steam parallelism at high, medium and low pressure between said         first steam generator GRV1 and said second steam generator GRV2,         the high pressure steam collector CAP, the medium pressure steam         collector CMP and the low pressure steam collector CBP being         respectively in fluid communication with steam lines at high         pressure AP, at medium pressure MP and at low pressure BP         through which the different stages of the TV steam turbine are         fed and     -   a generator coupled to the steam turbine.

According to this invention the plant also comprises valve means and similar means opening or closing which it is possible to change the working conditions of the plant. Said valve means are not illustrated in the figure scheme and are not detailed hereinafter since they are components well known to a technician of the sector.

Furthermore, according to this invention the plant comprises detection and check means to monitor and detect a plurality of parameters connected to the correct functioning and/or malfunctioning of said plant, particularly of the first and second gas turbine and generator groups TG1 and TG2, of the first and second steam generators GRV1 and GRV2 and of the steam turbine TV.

Advantageously, according to this invention the plant comprises a control and processing unit DCS (not illustrated for the sake of simplicity of representation) where to memorize:

-   -   each single functional groups sequence necessary to obtain the         start/stop of each component of the plant starting from off         and/or partial or total on conditions and     -   the different plant conditions which have to be detected by said         detection and check means to then give the green light to the         execution of the functional groups still to be executed.

Advantageously, said control and processing unit is connected to said detection and check means in order to:

-   -   acquire and process information concerning the functioning         and/or malfunctioning status of the components of the plant;     -   further to the request for a specific start/stop sequence among         the memorized start/stop sequences, start automatically and in         succession the functional groups of said specific sequence,         subordinate to the detection by said monitoring means of all the         different necessary plant conditions to be monitored in order to         allow the start-up of each functional group, by verifying the         correct execution of each functional group started up.

As above detailed, in the plant control and processing unit in addition to the functional groups it is possible to memorize also the sequences of functional groups, i.e. more functional groups linked between them according to an optimal and set sequence, corresponding to the different start up or stop procedures, both total or partial, of the plant according to the invention. At the same time, in said plant control and processing unit it is also possible to memorize the specific and different local conditions in the different plant components and in the remaining parts of the plant itself to be detected to give the green light for execution of the functional groups still to be executed. This is possible thanks to the fact that the plant control and processing unit continuously detects the specific and different local conditions of the plant components and in the remaining parts of the plant itself while comparing the detected values with the reference values (i.e. suitable to give the green light) and by finding a value correspondence allows the automatic starting of the following functional groups of the specific start/stop sequence required. Substantially, the plant control and processing unit allows the automatic and linked execution of the different functional groups that compose the required sequence thanks to a systematic and automatic control suitable to give the green light to the execution of a specific functional group as soon as the values detected by the control and detection means meet the requirements memorized in the control and processing unit to give the consensus for the execution of the functional groups still to be executed.

Therefore, in the plant according to this invention, the linkage between the different functional groups necessary to have a start or stop sequence, total or partial, of the plant does not depend anymore on the experience and free will of the plant operator, but is assured in its best and repeatable form, by the control and processing unit of the plant.

We will detail hereinafter some preferred example embodiments according to this invention in relation to some sequences of functional groups necessary to pass from a first operational configuration to a second operational configuration.

A. Start-up of a First as Turbine and Generator Group TG1 and of the Steam Turbine TV from an Off State.

The start up phases of a first gas turbine and generator group TG1 and of the steam turbine TV of the plant comprise the following functional groups sequence:

-   -   GF1A: Prearrange the start up of said first gas turbine and         generator group TG1;     -   GF2A: Start up of said first gas turbine and generator group TG1         and pressurization of said first steam generator GRV1;     -   GF3A: Warm up and load increase of said steam turbine TV after         the starting of said first gas turbine and generator group TG1         with vacuum in the condenser;

In the plant according to this invention, this start up sequence is characterized in that it comprises the following phases:

-   -   verifying through said detection and check means the actual         completion of operating group GF1A (prearrangement of the         start-up of said first gas turbine and generator group TG1) and,         subordinate to the fulfilment of that condition, to operate the         automatic start-up of the sequence of said functional group GF2A         which determines the start-up of said first gas turbine and         generator group TG1 and the pressurization of said first steam         generator GRV1 and     -   verifying through said detection and check means the actual         completion of functional group GF2A (start-up of said first gas         turbine and generator group TG1 and the pressurization of said         first steam generator GRV1) and, subordinate to the fulfilment         of that condition, to operate the automatic start-up of the         sequence of said functional group GF3A which determines the warm         up and the load increase of steam turbine TV.         B. Start up of a Second Gas Turbine and Generator Group TG2 with         a First Gas Turbine and Generator TG1 Group and Steam Turbine TV         Already Operating

The start-up phases of a second gas turbine and generator group TG2 comprise, in order, the following sequence of functional groups:

-   -   GF4A: prearrangement of the start up of said second gas turbine         and generator group TG2     -   GF5A: Start-up of said second gas turbine and generator group         TG2 and pressurization of said second steam generator GRV2 and     -   GF6A: Insertion of a steam parallelism between said second steam         generator GRV2 and said first steam generator GRV1 through said         steam collectors at high CAP, medium CMP and low CBP pressure         respectively feeding said high, medium and low pressure stages         of said steam turbine TV.

In the plant according to the invention, said start up sequence is characterized in that it comprises the following phases:

-   -   to verify through said detection and check means the actual         achievement of the plant conditions to be achieved as a         consequence of the correct execution of said functional group         GF1A (operating the start-up of said first gas turbine and         generator group TG1) and, subordinate to the fulfilment of that         condition, to determine the automatic start-up of the sequence         of said functional group GF4A which operates the start-up of         said second gas turbine and generator group TG2;     -   verifying through said detection and check means the actual         achievement of the plant conditions to be achieved as a         consequence of the correct functioning of said functional group         GF3A (warm up and load increase of said steam turbine TV         following the start-up of the first gas and generator turbine         TG1) and, subordinate to the achievement of that condition,         determining the automatic start-up of the sequence of said         functional group GF5A which determines the start-up of the         second gas turbine and generator group TG2 and the         pressurization of the second steam generator GRV2, and     -   checking through said detection and check means the actual         completion of said functional group GF5A (start-up of the second         gas turbine and generator group TG2 and the pressurization of         the second steam generator GRV2) and, subordinate to the         achievement of that condition, determining the automatic         start-up of the sequence of said functional group GF6A which         starts a steam parallelism between the second steam generator         GRV and the first steam generator GRV1,

C. Stop of the Second Gas Turbine and Generator Group (TG2) While the First Gas Turbine and Generator Group TG1 and Steam Turbine TV are Working

The stopping phases of the second gas turbine and generator group TG2 and of the second steam generator GRV2 while the first gas turbine and generator group TG1 and steam turbine TV are still working comprise the following sequence of functional groups:

-   -   GF4B: interruption of the steam parallelism between the second         steam generator GRV2 and the first steam generator GRV1 and     -   GF3B: stopping of the second gas turbine and generator group         TG2.

In the plant according to this invention, this stop sequence is characterized in that it comprises the following phases:

-   -   verifying through said detection and check means the actual         completion of said functional group GF4B (interruption of the         steam parallelism of the second steam generator GRV2 with the         first steam generator GRV1) and, subordinate to the fulfilment         of that condition, operating the automatic start-up of the         sequence of said function group GF3B for the stopping of the         second gasturbine and generator group TG2.

Preferably, said functional group GF3B (stopping of the second gas turbine and generator group TG2) comprises a simultaneous bottling of the second steam generator GRV2 to keep steam pressure and temperature as long as possible inside.

D. Total Stop of the Plant Starting from a Condition Where Only the First as Turbine and Generator TG1 and the Steam Turbine TV are Working

The total stop phases of the plant starting from a condition where only the first gas turbine and generator TG1 and the steam turbine TV are working comprise the following sequence of functional groups:

-   -   GF2B: Load reduction of the first gas turbine and generator         group TG1 and block of the steam turbine (TV) and     -   GF1B: Stopping of the first gas turbine and generator group TG1.

In the plant according to this invention, this stop sequence is characterized in that it comprises the following phases:

-   -   verifying through said detection and check means the actual         completion of said functional group GF2B (load reduction of said         first gas turbine and generator group TG1 and block of the steam         turbine TV) and, subordinate to the fulfilment of that         condition, determining the automatic start-up of the sequence of         said functional group GF1B for the stopping of the first gas         turbine and generator group TG1.

Preferably said functional group GF1B (stopping of said first gas turbine and generator group TG1) comprises a simultaneous bottling of the first steam generator GRV1 to keep steam pressure and temperature as long as possible inside.

As can be appreciated from what has been described, the method according to the present invention, and the plant according to the present invention, allow meeting above mentioned need and at the same time overcoming the drawbacks referred to in the introductory part of the present description with reference to the prior art. As a matter of fact, as already mentioned, the linkage between the different functional groups necessary to have a start or stop sequence, is not left anymore to the free will of the plant's operator, but is guaranteed in an optimal and repeatable way, by the control and processing unit of the plant.

Obviously, a technical expert, may apply several modifications and arrangements to the above detailed method and plant in order to satisfy contingent and specific needs but without exceeding the range of the protection of the present invention as defined by the following claims. 

1. A method to start up and manage a combined cycle thermal plant for energy production comprising a first gas turbine and generator group (TG1), a first steam generator (GRV1), a multistage steam turbine (TV) and a generator coupled to said steam turbine (TV) wherein: said first steam generator (GRV1) is a recovery steam generator to regenerate the latent heat of the exhaust gases of said first gas turbine and generator group (TG1); said first steam generator (GRV1) is in fluid communication through steam lines at high, medium and low pressure with corresponding stages at high, medium and low pressure of said steam turbine (TV) and said generator is kinematic coupled to said steam turbine to be rotationally operated; said plant comprises detection and check means to monitor and detect a plurality of parameters connected to the correct functioning and/or malfunctioning of said first gas turbine and generator group (TG1), of said first steam generator (GRV1) and, respectively of said steam turbine (TV), wherein the start-up phases of the plant starting from an off-state comprise, in order, the following sequence of functional groups: GF1A: prearranging said first gas turbine and generator group (TG1) for start-up; GF2A: Start-up of said first gas turbine and generator group (TG1) and pressurization of said first steam generator (GRV1); GF3A: Warm up and load increase of said steam turbine (TV) following the start-up of said first gas turbine and generator group (TG1) and vacuum to the capacitor; characterized in that it comprises the following phases: verifying through said detection and check means the actual completion of said operating unit GF1A for the prearrangement of the start-up of said first gas turbine and generator group (TG1) and, subordinate to the fulfilment of this condition, to operate the automatic start-up of the sequence of said functional group GF2A which determines the start-up of said first gas turbine and generator group (TG1) and the pressurization of said first steam generator (GRV1) and verifying through said detection and check means the actual completion of said functional group GF2A for the start-up of said first gas turbine and generator group (TG1) and the pressurization of said first steam generator (GRV1) and, subordinate to the fulfilment of that condition, to operate the automatic start-up of the sequence of said functional group GF3A which determines the warm up and the operating of said steam turbine (TV), so that the whole start-up sequence is automatically carried out.
 2. The method of claim 1, wherein said combined cycle thermal plant for energy production further comprises: a second gas turbine and generator group (TG2), a second recovery steam generator (GRV2) to regenerate the latent heat of the exhaust gases of said second gas turbine and generator group (TG2); said second steam generator (GRV2) being in fluid communication through a high pressure steam collector (CAP), through a medium pressure steam collector (CMP) and through a low pressure steam collector (CBP) with said high, medium and low pressure steam lines of said first steam generator (GRV1) to feed said high, medium and low pressure stages of said steam turbine (TV) through a steam parallelism at high, medium and low pressure between said first steam generator (GRV1) and said second steam generator (GRV2), said plant comprises detection and check means to detect and monitor a plurality of parameters connected to the correct functioning and/or malfunctioning of said second gas turbine and generator group (TG2) and of said second steam generator (GRV2), wherein the start-up phases of said second gas turbine and generator group (TG2) comprise, in order, the following sequence of functional groups: GF4A: to prearrange said second gas turbine and generator group (TG2) for start-up; GF5A: Start-up of said second gas turbine and generator group (TG2) and pressurization of said second steam generator (GRV2) and GF6A: Insertion of a steam parallelism between said second steam generator (GRV2) and said first steam generator (GRV1) through said steam collectors at high (CAP), medium (CMP) and low (CBP) pressure respectively feeding said high, medium and low pressure stages of said steam turbine (TV), characterized in that it comprises the phases of: verifying through said detection and check means the actual achievement of the plant conditions to be achieved as a consequence of the correct execution of said functional group GF1A which operates the start-up of said first gas turbine and generator group (TG1) and, subordinate to the fulfilment of that condition, to determine the automatic start-up of the sequence of said functional group GF4A which operates the start-up of said second gas turbine and generator group (TG2); verifying through said detection and check means the actual achievement of the plant conditions to be achieved as a consequence of the correct functioning of said functional group GF3A for the warm up and load increase of said steam turbine (TV) following the startup of said first gas and generator turbine (TG1) and vacuum of the condenser and, subordinate to the achievement of that condition, determining the automatic start-up of the sequence of said functional group GFSA which determines the start-up of said second gas turbine and generator group (TG2) and the pressurization of said second steam generator (GRV2) and checking through said detection and check means the actual completion of said functional group GFSA for the start-up of said second gas turbine and generator group (TG2) and the necessary pressurization of said second steam generator (GRV2) and, subordinate to the achievement of that condition, determining the automatic start-up of the sequence of said functional group GF6A which starts a steam parallelism between said second steam generator (GRV2) and said first steam generator (GRV1), so that the whole start-up sequence of said second gas turbine and generator group (TG2) is automatically carried out.
 3. The method of claim 2, wherein the stop phases of said second gas turbine and generator group (TG2) and of said second steam generator (GRV2) comprise, in order, the following sequence of functional groups: GF4B: Interruption of the steam parallelism between said second steam generator (GRV2) and said first generator (GRV1) and GF3B: Stopping of said second gas turbine and generator group (TG2) characterized in that it comprises the phases of: verifying through said detection and check means the actual completion of said functional group GF4B intended to interrupt the steam parallelism of said second steam generator (GRV2) with the steam of said first steam generator (GRV1) and, subordinate to the fulfilment of that condition, operating the automatic start-up of the sequence of said function group GF3B for the stopping of said second gas turbine and generator group (TG2), so that the whole stopping sequence of said second gas turbine and generator group (TG2) is automatically carried out.
 4. The method of claim 3, wherein said functional group GF3B intended to stop said second gas turbine and generator group (TG2) comprise a simultaneous bottling of said second steam generator (GRV2) to keep steam pressure and temperature as long as possible inside.
 5. The method of claim 1, 3 or 4 wherein the stop phases of said first gas turbine and generator group (GRV1) comprise, in order, the following functional groups sequence: GF2B: Load reduction of said first gas turbine and generator group (TG1) and block of said steam turbine (TV) and GF1B: Stopping of said first gas turbine and generator group (TG1) characterized in that it comprises the phases of: verifying through said detection and check means the actual completion of said functional group GF2B intended for the load reduction of said first gas turbine and generator group (TG1) and block of said steam turbine (TV) and, subordinate to the fulfilment of that condition, determining the automatic start-up of the sequence of said functional group GF1B for the stopping of said first gas turbine and generator group (TG1), so that the whole stop sequence of said first gas turbine and generator group (TG1) is automatically carried out.
 6. The method of claim 5, wherein said functional group GF1B intended for the stopping of said first gas turbine and generator group (TG1) comprises a simultaneous bottling of said first steam generator (GRV1) to keep steam pressure and temperature as long as possible inside.
 7. Combined cycle thermal plant to produce energy comprising: a first gas turbine and generator group (TG1), a first recovery steam generator (GRV1) to regenerate the latent heat of the exhaust gases of said first gas turbine and generator group (TG1); a steam turbine (TV) with high, medium and low stage in fluid communication with said first steam generator (GRV1) through high, medium and low pressure steam lines; a generator kinematic coupled to said steam turbine (TV)to be rotationally operated; detection and check means to monitor and detect a plurality of parameters connected to the correct functioning and/or malfunctioning of said plant, namely of said first gas turbine and generator group (TG1), of said first steam generator (GRV1) and, respectively of said steam turbine (TV), characterized in that it comprises a control and processing unit where to memorize: each single functional groups sequence necessary to obtain the start/stop of each component of the plant starting from off and/or partial or total on conditions and the different plant conditions which have to be detected by said detection and check means to then give the green light to the execution of the functional groups still to be executed, wherein said check and processing unit is connected to said detection and check means in order to: acquire and process information concerning the functioning and/or malfunctioning status of said plant; further to the request for a specific start/stop sequence among the memorized start/stop sequences, automatically start in succession the functional groups of said specific sequence subordinate to the detection by said monitoring means of all the different necessary plant conditions to be monitored by said detection and check means in order to allow the start-up of each functional group of the required sequence, by verifying the correct achievement of the plant conditions which can be achieved as a consequence of the correct execution of a functional group previous to starting the following functional group within the same specific sequence having been required.
 8. The plant of claim 7, further comprising a second gas turbine and generator group (TG2) and a second recovery steam generator (GRV2) to regenerate the latent heat of the exhaust gases of said second gas turbine and generator group (TG2); wherein: said second steam generator (GRV2) is in fluid communication through a high pressure steam collector (CAP), through a medium pressure steam collector (CMP) and through a low pressure steam collector (CBP) with said high, medium and respectively low pressure steam lines which feed said high, medium and low pressure stages of said steam turbine (TV) to create a steam high, medium and low pressure parallelism between said first steam generator (GRV1) and said second steam generator (GRV2), said plant comprises further detection and check means to detect and monitor a plurality of parameters connected to the correct functioning and/or malfunctioning of said second gas turbine and generator group (TG2) and of said second steam generator (GRV2) and said check and processing unit is connected to said further detection and check means to acquire and process information concerning the functioning and/or malfunctioning status of said second gas turbine and generator group (TG2) and of said second steam generator (GRV2).
 9. The plant of claim 8, wherein said first steam generator (GRV1) and said second steam generator (GRV2) are cylindrical body generator with horizontal development, with three different levels of pressure and degasification device. 